Aeronautical Communications Research Articles

Deep Learning Based Radio-Signal Identification With Hardware Design

This paper proposes a deep learning based intelligent method for detecting and identifying radio signals considering two applications: first, cognitive radar for identifying micro unmanned aerial systems and second, an automated modulation classification scheme for cognitive radio, which can be used for aeronautical communication systems. Our proposed intelligent method is designed of a spectral correlation function based feature extractor and a low-complexity deep belief network classifier with low FPGA logic utilization.

Studying crashes to avoid clashes: A translational approach to develop terminological competence for aeronautic communication

Miscommunication in the cockpit or between pilots and air traffic controllers (ATCs) could be fatal when they use English, the de facto language for international civil aviation. To ensure air safety, the International Civil Aviation Organization (ICAO) has set up English proficiency requirements in Document 9835, calling for adherence to standardized terminology in aeronautic communication. For this reason, terminological competence proves a crucial challenge to non-native speakers of English and merits study from a variety of perspectives. Drawing from relevant work, the current study reports on a translational approach to developing terminological competence for student pilots attending a terminology course tailored to ICAO standards. By extracting subtitles from Mayday, a documentary series on air crashes, near-crashes, and crises, we built a specialized bilingual parallel corpus on aviation and analyzed terminological data against the inventory of events, domains, and sub-domains specified in Document 9835. Through the identification, elaboration, translation, and management of specialized terms, we explore the terminological competence development, and through follow-up interviews we identify the features of this course in shaping student pilots into domain experts qualified for aeronautic communication.

New Spectrum Efficient Reconfigurable Filtered-OFDM Based L-Band Digital Aeronautical Communication System

To meet an ever-increasing demand of the spectrum for aeronautical communication, we propose new L -band digital aeronautical communication system using reconfigurable filtered orthogonal frequency division multiplexing. The proposed protocol enables transceivers to dynamically adapt the transmission bandwidth over a wide range to meet the desired quality of service, and high out-of-band attenuation leads to significant improvement in the vacant spectrum utilization. We support our claims via simulation and complexity comparison results for various realistic channel conditions.

Outage Analysis and Finite SNR Diversity-Multiplexing Tradeoff of Hybrid-Duplex Systems for Aeronautical Communications

A hybrid-duplex aeronautical communication system (HBD-ACS) consisting of a full-duplex-enabled ground station (GS) and two half-duplex (HD) air stations (ASs) is proposed as a direct solution to the spectrum crunch faced by the aviation industry. The closed-form outage probability and finite signal-to-noise ratio (SNR) diversity gain expressions in aeronautical communications over Rician fading channels are derived for a successive interference cancellation (SIC) detector. Similar expressions are also presented for an interference ignorant (II) detector and the HD-equivalent modes at GS and ASs. Through the outage and finite SNR diversity gain analysis conducted at the nodes, and system level, residual self-interference (SI) and inter-AS interference are found to be the primary limiting factors in the proposed HBD-ACS. Further investigations revealed that the II and SIC detectors in the proposed HBD-ACS are suitable for the weak and strong interference scenarios, respectively. When compared with the HD-ACS, the proposed HBD-ACS achieves a lower outage probability and higher diversity gains at higher multiplexing gains when operating at low SNRs. The finite SNR analysis also showed the possibility of the proposed HBD-ACS being able to attain interference-free diversity gains through proper management of the residual SI. Hence, the proposed HBD-ACS is more reliable and can provide a better throughput compared with the existing HD-ACS at low-to-moderate SNRs.

Impact Assessment of the L-Band Digital Aeronautical Communications System on the Joint Tactical Information Distribution System

The L-band digital aeronautical communications system (LDACS) is the future air–ground communications technology currently undergoing the International Civil Aviation Organization standardization process. As LDACS is intended to operate in the frequency band 960–1164 MHz, compatibility tests between LDACS and the legacy systems operating in this frequency band are necessary to ensure that no system is harmfully interfered. One of these systems is the joint tactical information distribution system (JTIDS), a technology employed by the tactical data link Link 16. In this paper, we present the results of an impact assessment of LDACS on JTIDS conducted through simulations. The extent of the impact has been quantified by simulating a wide variety of interference configurations, which are expected to cover most realistic interference conditions between LDACS and JTIDS. Baseband simulation models of both systems have been implemented and an interference scenario between LDACS and JTIDS has been defined. To evaluate the impact, the degradation of the signal-to-noise ratio (SNR) of JTIDS by the presence of LDACS has been determined. Default JTIDS transmissions, where the information is repeated at distant frequencies, do not show a significant degradation by the presence of strong LDACS interference, with an SNR loss lower than 1 dB in any considered interference scenario. Comparatively, a certain dependency on the specific LDACS deployment is noticeable for less protected JTIDS transmissions. Based on the observed interdependencies, recommendations for the deployment of LDACS are given in this paper, such that the impact of LDACS on JTIDS is minimized.

Adaptive Coherent/Non-Coherent Single/Multiple-Antenna Aided Channel Coded Ground-to-Air Aeronautical Communication

In this treatise, first of all, we conceive a generic multiple-symbol differential sphere detection (MSDSD) solution for both single- and multiple-antenna-based noncoherent schemes in both uncoded and coded scenarios, where the high-mobility aeronautical Ricean fading features are taken into account. The bespoke design is the first MSDSD solution in the open literature that is applicable to the generic differential space-time modulation (DSTM) for transmission over Ricean fading. In the light of this development, the recently developed differential spatial modulation and its diversity counterpart of differential space-time block coding using index shift keying are specifically recommended for aeronautical applications owing to their low-complexity single-RF and finite-cardinality features. Moreover, we further devise a noncoherent decision-feedback differential detection and a channel-state information estimation aided coherent detection, which also take into account the same Ricean features. Finally, the advantages of the proposed techniques in different scenarios lead us to propose for the aeronautical systems to adaptively: 1) switch between coherent and non-coherent schemes; 2) switch between single- and multiple-antenna-based schemes as well as; and 3) switch between high-diversity and high-throughput DSTM schemes.

Seamless handover for video streaming over an SDN-based Aeronautical Communications Network

There have been increasing interests in applying Software Defined Networking (SDN) to aeronautical communications primarily for air traffic management purposes. From the service passenger communications' point of view, a major goal is to improve passengers' perception of quality of experience on the infotainment services being provided for them. Due to the high speed of aircrafts and the use of multiple radio technologies during different flight phases and across different areas, vertical handovers between these different radio technologies are envisaged. This poses a challenge to maintain the quality of service during such handovers, especially for high bandwidth applications such as video streaming. This paper proposes an SDN-based aeronautical communications architecture consisting of both satellite and terrestrial-based radio technology. In addition, an experimental implementation of the Locator ID Separation Protocol (LISP) protocol with built-in multi-homing capability over the SDN-based architecture was proposed to handle vertical handovers between the satellite and other radio technologies onboard the aircraft. By using both objective and subjective Quality of Experience (QoE) metrics, the simulation experiments show the benefit of combining LISP with SDN to improve the video streaming quality during the handover in the aeronautical communication environment.

Speaker Identification for OFDM-Based Aeronautical Communication System

Although a lot of research has been done on speaker identification in the presence of noise and channel variation, to the best of our knowledge, no work has been reported for aeronautical applications. In this paper, we aim to fulfill this goal by developing a Speaker Identification System (SIS) for future aeronautical communications systems. Furthermore, we present a novel feature extraction scheme based on multi-resolution analysis. The proposed features called SMFCC use Mel Frequency Cepstral Coefficients (MFCCs) features of stationary wavelet transform sub-bands. The extracted features are modeled using the i-vector approach, and support-vector machines are adopted as a back-end classifier. The performance of the proposed SIS is evaluated using two publicly available databases. Comparison of the proposed approach with the baseline MFCC feature extraction shows the feasibility and the robustness of the proposed method. Besides the noise reduction, the identification accuracy is improved by about 12% at higher signal-to-noise ratios and reaches 97.33% as compared to 88.33% using MFCC for ATCOSIM database.

A Comprehensive Survey on UAV Communication Channel Modeling

Unmanned aerial vehicles (UAVs) have stroke great interested both by the academic community and the industrial community due to their diverse military applications and civilian applications. Furthermore, UAVs are also envisioned to be part of future airspace traffic. The application functions delivery relies on information exchange among UAVs as well as between UAVs and ground stations (GSs), which further closely depends on aeronautical channels. However, there is a paucity of comprehensive surveys on aeronautical channel modeling in line with the specific aeronautical characteristics and scenarios. To fill this gap, this paper focuses on reviewing the air-to-ground (A2G), ground-to-ground (G2G), and air-to-air (A2A) channel measurements and modeling for UAV communications and aeronautical communications under various scenarios. We also provide the design guideline for managing the link budget of UAV communications taking account of link losses and channel fading effects. Moreover, we also analyze the receive/transmit diversity gain and spatial multiplexing gain achieved by multiple-antenna-aided UAV communications. Finally, we discuss the remaining challenge and open issues for the future development of UAV communication channel modeling.

A Review of Recent Advances and Security Challenges in Emerging E-Enabled Aircraft Systems

The continuing increase in air traffic, along with airline operators gradually adopting IP-based network technologies, has led to the transformational concept of e-Enabled or “connected” aircraft. This new framework envisions a single aeronautical communications architecture connecting across the entire spectrum of the aviation sector. However, due to the complex and multidimensional nature of aviation operations, no single technology can achieve the above goal. Instead, building an integrated system which uses multiple communication protocols and architectures, as well as cloud computing and big data analytics, is the most promising way forward. Hence this paper surveys the latest trends in emerging network communication systems for commercial aviation. A range of cyber-threats is then identified for the e-Enabled aircraft paradigm, followed by discussions on related solution methodologies. Note that the topics related to military aviation security are not considered here.

Designing the Radiotelephony Plain English Corpus (RTPEC): A specialized spoken English language corpus towards a description of aeronautical communications in non-routine situations

Pilots and air traffic controllers need to undergo a specific English test in order to be granted a license for international operations. A language proficiency scale was developed to serve as a parameter to all aviation regulatory agencies throughout the world by targeting the language produced specifically by air traffic controllers and pilots in radio communications when non-routine situations (such as technical problems, bird strike, changes in weather, health problems on board, etc.) occur (ICAO 2010). However, there is a lack of empirical investigation which could shed light upon this particular register helping the users of the scale with its understanding. In an attempt to fill this gap, this paper outlines a compilation of the Radiotelephony Plain English Corpus (RPTEC), a spoken corpus of aeronautical communication consisting of transcriptions of exchanges between pilots and air traffic controllers in non-routine situations for research and pedagogical purposes. By presenting steps taken during the process, we intend to provide fellow researchers with data which may suit other purposes and yield further analyses, as well as enlighten similar investigations in the field of English for Specific Purposes.

Gaussian Mixture Learning for LDPC Coded BICM Receivers With Blanking Nonlinearity

With the aid of blanking nonlinearity, the low density parity check (LDPC) coded bit-interleaved coded modulation (BICM) has been jointly considered as a robust mitigation for the impulsive interference in orthogonal frequency division multiplexing (OFDM) systems. However, the Gaussian assumption for the nonlinear channel conditional probability induces the mismatched L-values in the conventional MAP demodulator. In this paper, combined with the pulse blanking optimization via the PEXIT analysis, we propose a novel MAP demodulator based on the Gaussian mixture model (GMM) and estimate the parameters with the expectation-maximization (EM) algorithm. Taking the L-band Digital Aeronautical Communication System Type1 (L-DACS1) as an example, the GMM-based MAP demodulator can obtain the PEXIT thresholds that match the decoding curves well and provide the better BER performance in the interference-limit channel environment.

Trend of Aeronautical Communication Systems for Safety

Trend of Aeronautical Communication Systems for Safety

Advances in Opportunistic Scheduling in IEEE 802.16 WiMAX for Aeronautical Communication Networks

The demand for faster internet connections to access wireless multimedia applications, Aeronautical Communication Networks (ACNs) and internet services has resulted into rise of developing broadband wireless technologies in recent years. The demand for higher data rates was the backbone for developing wireless communication technologies such as Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE) and High-Speed Packet Access (HSPA). The big challenge with wireless communications lies with providing Quality of Service (QoS) under various environmental challenges and maximizing resource utilization at the same time. In wireless communication, the support for QoS is difficult due to the unpredictable nature of wireless channels. Opportunistic Scheduling plays a big role towards meeting QoS requirements and managing resources in aeronautical communication networks. Various opportunistic schedulers focus on increasing the system capacity of a wireless communication network, while some aim on improving the system’s fairness and throughput. With such interest in opportunistic scheduling, the paper focuses on reviewing recently proposed opportunistic scheduling algorithms, the objectives they were designed for, and their shortcomings. An effective opportunistic scheduling algorithm with hierarchical modulation technique is presented in this paper. The algorithm focuses on the ability to allocate resources between two users with different channel conditions; that is a user with good channel conditions and a user with bad channel conditions, to maximize the system’s throughput and maintain fairness.

Feasibility of Cell Planning for the <italic>L</italic>-Band Digital Aeronautical Communications System Under the Constraint of Secondary Spectrum Usage

The L -band digital aeronautical communications system (LDACS) is a cellular air-ground data link for air traffic control. It is a cornerstone of the future aeronautical communications infrastructure. LDACS shall operate in the frequency band 960–1164 MHz under the constraint of secondary spectrum usage. This implies strict spectral, power, and spatial separation toward current legacy systems operating in this frequency band. It has been proposed to fulfil these restrictions using cell planning for LDACS without changing frequency allocations of the legacy systems. However, the feasibility of such a cell planning is yet to be demonstrated. In this paper, we demonstrate the feasibility of LDACS cell planning under these constraints. For this purpose, we introduce the theoretical limits for such a separation enabling the coexistence of LDACS and distance measuring equipment (DME: the primary user) system in the same frequency band. Closed-form expressions are obtained such that the proper operation of DME is not harmfully affected by LDACS. These expressions are utilized in the first step to find DME-compliant locations for LDACS ground stations. In the second step, interference constraints within LDACS itself are defined and applied. This approach yields DME-compliant locations of LDACS ground stations with channel assignments fulfilling the interference constraints. The application of our method shows that LDACS cell planning in Europe is possible without disturbing the proper operation of the DME system.

Regularized Zero-Forcing Precoding-Aided Adaptive Coding and Modulation for Large-Scale Antenna Array-Based Air-to-Air Communications

We propose a regularized zero-forcing transmit precoding (RZF-TPC)-aided and distance-based adaptive coding and modulation (ACM) scheme to support aeronautical communication applications, by exploiting the high spectral efficiency of the large-scale antenna arrays and link adaption. Our RZF-TPC-aided and distance-based ACM scheme switches its mode according to the distance between the communicating aircraft. We derive the closed-form asymptotic signal-to-interference-plus-noise ratio (SINR) expression of the RZF-TPC for the aeronautical channel, which is Rician, relying on a non-centered channel matrix that is dominated by the deterministic line-of-sight component. The effects of both realistic channel estimation errors and of the co-channel interference are considered in the derivation of this approximate closed-form SINR formula. Furthermore, we derive the analytical expression of the optimal regularization parameter that minimizes the mean square detection error. The achievable throughput expression based on our asymptotic approximate SINR formula is then utilized as the design metric for the proposed RZF-TPC-aided and distance-based ACM scheme. Monte-Carlo simulation results are presented for validating our theoretical analysis as well as for investigating the impact of the key system parameters. The simulation results closely match the theoretical results. In the specific example that two communicating aircrafts fly at a typical cruising speed of 920km/h, heading in opposite direction over the distance up to 740km taking a period of about 24 min, the RZF-TPC-aided and distance-based ACM is capable of transmitting a total of 77 GB of data with the aid of 64 transmit antennas and four receive antennas, which is significantly higher than that of our previous eigen-beamforming transmit precoding-aided and distance-based ACM benchmark.

M-pulse amplitude modulation of a flat-topped beam for aeronautical laser communications.

Using the Rytov method, bit error rate (BER) performances of M-pulse amplitude modulation (M-PAM) are investigated for a flat-topped beam when such a beam is employed in an aeronautical laser communication system operating in vertical paths having weak atmospheric turbulence. By using the on-axis scintillation index and the log-normal distributed intensity, the average BER (⟨BER⟩) is evaluated for M-PAM when M=2,4,8. The scintillation indices of collimated flat-topped beams of various flatness orders N are compared against propagation lengths, source sizes, and zenith angle for laser communication vertical paths, including uplink and downlink. Also, the ⟨BER⟩ versus the average signal to noise ratio (⟨SNR⟩) is examined for various beam flatness orders. It is shown that as the flatness order increases, the scintillation index decreases. Taking one of the best flatness order values, N=15, for reducing the scintillations, ⟨BER⟩ versus propagation lengths, source sizes, zenith angle, and ⟨SNR⟩ are found for various values of M. When M is increased, the ⟨BER⟩ is found to deteriorate.

Efficient Spectrum Sensing for Aeronautical LDACS Using Low-Power Correlators

Air traffic has seen tremendous growth over the past decade pushing the need for enhanced air traffic management schemes. The $L$ -band digital aeronautical communication system (LDACS) is gaining traction as a scheme of choice, and aims to exploit the capabilities of modern digital communication techniques and computing architectures. Cognitive radio-based approaches have also been proposed for LDACS to improve spectrum efficiency and communication capacity; however, these require intelligent compute capability in aircrafts that enforce limited space and power budgets. This paper proposes the use of multiplierless correlation to enable spectrum sensing in LDACS air-to-ground links, and its integration into the on-board LDACS system. The proposed architecture offers improved performance over traditional energy detection (ED) even at low signal-to-noise ratio (SNR) with lower energy consumption than a multiplier-based correlator, while also assisting in receiver synchronization. We evaluate the proposed architecture on a Xilinx Zynq field-programmable gate array and show that our approach results in 28.3% reduction in energy consumption over the multiplier-based approach. Our results also show that the proposed architecture offers 100% accuracy in detection even at −12-dB SNR without requiring additional circuitry for noise estimation, which are an integral part of ED-based approaches.

Ambiguity Function Analysis for OFDM-Based LDACS Passive Multistatic Radar

The ambiguity function analysis is central to investigating the resolution capabilities of a radar system. It is particularly important for passive radar scenarios, where the signals of opportunity have not been originally designed for radar purposes. This paper focuses on studying the achievable resolution capabilities for a noncoherent orthogonal frequency division-multiplexing (OFDM)-based passive multistatic radar for L-band digital aeronautical communication system (LDACS) signals. For this purpose, the ambiguity function obtained when employing the OFDM-based LDACS communications signals as signals of opportunity is studied. A generic bistatic link is considered and closed-form expressions for the expectation of the corresponding ambiguity function when accounting for the different signal contributions are derived. The resulting expressions are then used to evaluate and analyze the overall multistatic radar ambiguity function for two sample radar scenarios. The results highlight the impact of the geometry on the shape of the ambiguity function, allowing therefore for a better understanding of the effect that the geometry has on the range and velocity resolution capabilities of the studied system.

A Hardware-Efficient Synchronization in L-DACS1 for Aeronautical Communications

L-band digital aeronautical communication system type-1 (L-DACS1) is an emerging standard that aims at enhancing air traffic management by transitioning the traditional analog aeronautical communication systems to the superior and highly efficient digital domain. L-DACS1 employs modern and efficient orthogonal frequency-division multiplexing (OFDM) modulation technique to achieve more efficient and higher data rate in comparison to the existing aeronautical communication systems. However, the performance of OFDM systems is very sensitive to synchronization errors such as symbol timing offset (STO) and carrier frequency offset (CFO). STO and CFO estimations are extremely important for maintaining orthogonality among the subcarriers for the retrieval of information. This paper proposes a novel efficient hardware synchronizer for L-DACS1 systems that offers robust performance at low power and low hardware resource usage. Monte Carlo simulations show that the proposed synchronization algorithm provides accurate STO estimation as well as fractional CFO estimation. Implementation of the proposed synchronizer on a widely used field-programmable gate array (FPGA) (Xilinx xc7z020clg484-1) results in a very low hardware usage which consumed 6.5%, 3.7%, and 6.4% of the total number of lookup tables, flip-flops, and digital signal processing blocks, respectively. The dynamic power of the proposed synchronizer is below 1 mW.